In recent years, in order to improve the fuel efficiency and other performances of vehicles, development has been carried out on a vehicle having an idling stop function that stops the internal combustion engine when the vehicle is stationary. An automatic transmission mounted on such a vehicle having the idling stop function is provided with an electric oil pump that is electrically driven independently of a mechanical oil pump that is driven by the internal combustion engine, in order to prevent delay in supplying an engagement pressure to a clutch, a brake, and so on when starting the internal combustion engine to start the vehicle. Thus, even when the internal combustion engine is not in running, a hydraulic pressure is supplied from the electric oil pump.
On the other hand, the mainstream automatic transmissions have been automatic transmissions for typical conventional vehicles, that is, vehicles without the idling stop function, and therefore are not designed to have an electric oil pump mounted thereon. In the case of mounting such an automatic transmission on a vehicle with the idling stop function, it has been common to attach an electric oil pump externally to a transmission case of the automatic transmission (see, for example, Patent Document 1).